An engine for an automobile, for example, has been conventionally provided with an exhaust gas recirculation apparatus, in which a part of exhaust gas flowing in an exhaust pipe is introduced, as exhaust gas recirculation gas (i.e., “EGR gas”), into an intake pipe, and an in-cylinder maximum combustion temperature is decreased by mixing the EGR gas with intake air, thereby reducing harmful substance (e.g., nitrogen oxide) contained in the exhaust gas.
Such an exhaust gas recirculation apparatus includes an EGR piping for connecting an exhaust system and an intake system to each other in an engine, and an EGR valve housed inside of the EGR piping with an opening position thereof being adjustable. That is to say, a free wheel quantity of the EGR gas is adjusted by adjusting the opening position of the EGR valve.
In the exhaust gas recirculation apparatus of this type, deposits of a combustion product (such as oxide or carbide) contained in the EGR gas may be possibly produced in the EGR piping, for example, an exhaust gas free wheel channel formed inside of a circularly cylindrical nozzle fitted into a valve housing. Such deposits are caused by hydrocarbon (abbreviated as “HC”), carbon (abbreviated as “C”), or oil contained in the exhaust gas, and unfavorably adhere onto the outer periphery of the EGR valve, a drive shaft of the EGR valve and an inner wall of the exhaust gas free wheel channel, and the like due to the high viscosity. In the case where the deposits (i.e., sediments) adhere between the outer periphery of the EGR valve and the inner wall of the free wheel channel or between the drive shaft and the inner wall of the free wheel channel, opening/closing operations of the EGR valve is prevented, thereby raising problems of an impossibility of favorable adjustment of an opening position of the EGR valve, an impossibility of supply of the EGR gas into the intake pipe, an impossibility of achievement of a proper free wheel quantity of the EGR gas, and the like. Particularly, the above-described inconveniences conspicuously occur in the case where a drive torque for opening/closing the EGR valve is small or the opening position of the EGR valve is to be controlled within a finely angular range.
In order to solve the above-described problems, Patent Document 1 (i.e., Japanese Patent Laying-Open No. 2004-162665) has been proposed. Patent Document 1 discloses that an EGR valve is opened/closed by a predetermined opening position near a valve fully closed position while an engine stops (hereinafter this operation is referred to as “a valve reciprocating motion control operation”). As a consequence, adhering deposits are scraped by the EGR valve, thus eliminating or preventing any fixation of the EGR valve.
Otherwise, Patent Document 2 (i.e., Japanese Patent Laying-Open No. 2000-320347) discloses a reciprocating motion of a throttle valve within a predetermined range including the front and back of a fully closed position of the throttle valve in an operation for eliminating the fixation of the throttle valve caused by deposits. In other words, Patent Document 2 discloses “a valve reciprocating motion control operation” directed to the throttle valve.
However, neither of Patent Document 1 and 2, described above, consider the case where the deposits cannot be scraped even by “the valve reciprocating motion control operation” due to the strong fixation of the valve caused by the deposits, thereby raising problems, as follows:
Namely, the valve reciprocating motion control operation disclosed in Patent Document 1 is designed to be continued until a maximum current value of a motor current to be supplied to a drive motor is decreased down to a predetermined current value or lower. However, in a situation in which the maximum current value of the motor current is not decreased down to the predetermined current value or lower due to the strong fixation of the valve, the drive motor is unfavorably continued to be electrified, thereby making it difficult to shorten a time required for the control operation, achieve high efficiency and save power consumption.
In the meantime, the valve reciprocating motion control operation disclosed in Patent Document 2 is designed to first supply a drive current to a direct-acting torque motor in such a manner as to open a valve from a valve opening position at 0° (i.e., a fully closed position) to a valve opening position at 3° on a plus side. Here, in a situation in which the valve cannot be opened up to the position at 3° due to the strong fixation of the valve, the drive current is unfavorably continued to be supplied to the direct-acting torque motor. Also in this situation, the valve reciprocating motion control operation is continued for a long period of time, thereby making it difficult to shorten a time required for the control operation, achieve high efficiency and save power consumption.